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The media frequently reports that airlines have been cutting back on fuel to save money. How true is this, and is the practice unsafe?

It is true that carriers are, in some situations, cutting back on the carriage of extra fuel, which is heavy and therefore expensive to haul around. A fleetwide optimization helps them save money. But note that term: extra fuel.

Determining how much fuel will be carried on a given flight is a somewhat scientific undertaking, with some hard-and-fast rules. Crews do not ballpark how much they need with a cursory glance at a gauge, as you might do in a car before a road trip. The numbers are wrangled backstage, so to speak, by an airline’s dispatchers and flight planning staff; intended routing and altitude are balanced against wind and weather conditions.

The regulations get complicated, particularly on international routes, but a good place to start is the US domestic rule, which goes like this: You cannot take off without enough fuel to reach your intended destination, then proceed to the most distant of any required alternate airport (one or more might have to be designated, in accordance with forecast weather), plus maintain a 45-minute cushion on top of that.

That’s fuel enough to reach your destination; fly to your alternate; and fly for another 45 minutes on top of that. This is non-negotiable. You cannot—cannot—depart with less. Trust me, no airline that wants to remain in business asks its crews to do so, and if it did, no captain who wants to keep his or her license would agree.

Once underway, totals are monitored both by the pilots and on-the-ground dispatchers (the latter receive periodic updates via radio or automatic datalink transmission). Remaining fuel is compared to predetermined target values as the flight progresses.

Payload permitting, however, you are welcome to depart with more than is legally needed. A fatter margin gives you greater flexibility, i.e. holding time, in the event of unexpected delays. It’s this above-and-beyond fuel that airlines are (sometimes) cutting back on, not regulatory fuel.

It stands to reason that more gas is better than less. It provides greater time to troubleshoot problems or to wait out airborne holds, postponing the need to divert. But while cutbacks allow less wiggle room, they aren’t dangerous. The penalty isn’t crashing—it’s having to divert earlier than you’d like, resulting in hassles for passengers and crew.